Temperature compensator for inductance coils



June 27, 1944. o THOMPSON 2352,-458

TEMPERATURE COMPENSATOR FOR INDUCTANCE COILS Filed Oct. 15, 1942temperature-responsive coil substantially Petented June 27, 1944 UNITEDSTATES PATENT OFFICE TEMPERATURE COMPENSATOR FOR INDUCTANCE COILS ElmerO. Thompson, Grasmere, N. Y., assignor to Philco Radio and TelevisionCorporation, Philadelphia, Pal, a corporation of Delaware I ApplicationOctober 15, 1942, Serial No. 462,177

2 Claims.

This invention relates to inductance devices, and more particularly toinductance colls employed in radio and allied arts. i i

The principal object of the inventlon is to provide a novel device forcounteracting or compcnsating inductance variations of a coil, caused byambient temperature changes, or heating due to losses in the coilitself.

Another object of the invention is to provide, in combination with aninductance coil, a novel compensating -means for maintaining theeffective inductance of the constant, despite temperature changes. i

A further object of the invention is to provide a simple, inexpensiveand highly efiicient device for accomplishing the above-stated purpose.

Another object of the invention is to provide a compensating devicewhich is free of conductive coupling with the coil and may be readilycontrolled. i

A still further object of the invention is to provide 'a compensatingdevice of the abovementioned 'character which 'may be readilymanufactured separately from an inductance coil and 'may be readilyattached to the coil unit in cooperative relation therewith. i

- Other objects and features of the invention will be apparenthereinafter.

In the accompanying drawing:

Figure 1 is a plan view of a device embodying the invention;

Figure 2 is a sectional View taken along line 2-2 of Fig. 1; and

Figure 3 is a sectional view taken along line 3--3 of Fig. 1.

Referring more particularly to the drawing. there is shown 'aninductance coil unit comprising a cylindrical support I ormed ofsuitable insulating material, such as a ceramic material, and a coil 2wound about the peripheral surface of the support and carried thereby.For the purpose of the present invention, the details of construction ofthe coil and its support are relatively unimportant.

In accordance with the present invention, there is provided an invertedU-shaped bracket 3 which is adapted to embrace an edge portion of thecoil support at one end thereof, as clearly shown in Fig. 2. Thisbracket may be formed of any suitable material. On the inner arm of theU-shaped bracket, there is provided a portion 4 which is adapted toengage the inner surface of the cylindrical support, as shown in Fig. 2.The outer arm of the bracket 3 is provided with a slot 5 through which afastening screw 6 may extend. The screw engages a. threaded opening inthe support l and serves, in cooperation with a Washer 1, to secure thebracket firmly to the coil support. The slot 5 permits verticaladjustment of the bracket for a purpose which will appear presently. Inthe illustration of Fig. 2, the bracket is shown in its lowermostposition, in which it seats upon the upper end of the coil support.

A rod or shaft 8 is carried by the inner arm of bracket 3 and preferablyis formed integrally therewith. This rod extends transversely of theaxis of the coil unit near the upper portion thereof, as shown in Fig.2. A closed conductor or loop 9 is rotatably carried by the rod 8.Preferably a single turn is used, although more than one turn could beused if desired. This loop or ring may be conveniently formed of copper,and it has substantial cross sectional dimensions, so that it ismechanically rigid and has very low electrical resistance. The rod 8 maybe made of conducting material and connected to the loop 9; or it may beinsulated therefrom, or made of insulating material. A thermalresponsivebimetallic element n in the form of a spiral (see Flg. 3) has its innerend 'fastened to the rod 8 and its outer end fastened to the loop 9.This element responds to temperature changes, and it expands orcontracts accordingly, rotating the loop 9 about the fixed rod I as anaxis. Since thermal-responsive elements of this type are well known, itsaction will be well understood.

The loop 9 is dlsposed in the magnetic field produced by the currentflowing in the inductance coil. consequently, the loop 9 is inductivelycoupled with coil 2 by virtue of the interlinkage of these elements byat least a portion of the magnetic flux associated with coil 2. Assumingthat the loop 9 is normally dlsposed as illustrated in Fig. 3, if theloop is rotated clockwise, a greater amount of the magn etic fiux willinterlink it with the coil 2. hand, if the loop 9 is rotatedcounterciockwise, a smaller flux interlinkage will result.

As will be well understood, the presence oi loop 9 in mutually inductiverelation with coil 2 will afiect the inductance of the coil. The twoelements may be considered as constitutlng an air core transformer, theloop 9 being eflectively a short-circuited secondary winding. By varyingthe position of loop 9 in relation to coil 2,

On the other.

the eftect of the loop upon the effective coil inductance may be varieddue to the varying fiux interlinkage above mentioned. The purpose of thethermal-responsive element o is to adjust the loop 9 according totemperature changes which tend to vary the coil inductance, so as tocompensate for such variations and maintain the effective coilinductance substantially constant. As mentioned above the rod may beinsulated from the ring or may be in conductive relation therewith.However, it will be understood that the use of a rod insulated from thering would result in a different degree of compensation in response to agven angular movement of the ring than would result if the rod is inconductive relation with the ring. Preferably, the loop 9 is disposed atan angle of about 45 with the axis of the coil unit at normaltemperature, as shown in Flg. 3.

By adjusting the loop 9 axally of the coil unit, the en'ect of the loopupon the coil inductance may be varied. as may be readily seen. This isaccomplished by adjustin bracket 3 in the manner above described.

By adjusting the normal position of the loop in relation to the coil,the desired effective inductance of the coil may be obtained, and it maybe caused to remain substantially constant over a wide variation oftemperature. Or, if desired, the loop may be used to effect controlledvariation of the coil inductance, in response to increments oitemperature change. Since the resistance of the loop I is very low, itdoes not substantially aflect the electrical properties oi' the coil.Moreover, the loop s is substantially unaflected by vibration, since itis rigid, of considerable mass, and is balanced about a fixed axis.Furthermore, the bimetallic element is preferably one havingconsiderable inherent rigidity and thereiore adds to the stability ofthe ring.

A structure oi the type illustrated has other advantages, particularlyfrom the standpoint of manuiacture. The compensating device may be madeand assembled as a unit separately from the coil and then attached tothe coil unit in a simple operation, as will be readily apparent. This,as is illustrated in the preferred embodiment, may be accomplished bythe provision of a threaded opening in the coil support to receive thefastening screw. The compcnsating device does not require a high degreeoi' accuracy or precision in manufacture, since it may be readilyadjusted after its assembly on the coil unit. Moreover, the device is ofsimple Construction, and may be manufactured very inexpensively.

It w'll be understood, of course, that the intion is not limited to thespecific structure illustrated, but is capable of modifications.particularly as to details, within the scope of the appended claims.

Iclaim:

1. In combination. a hollow coil support, a helical coil mountedthereon, a U-shaped bracket embracing an edge portion of said support atone end thereof. a rod carried by the inner arm of said bracket andextending transversely within said support, a conductive loop rotatablycarried by said rod, and a thermal-responsive spiral element surroundingsaid rod and having its ends connected respectively to the rod and tosaid loop, said element serving to rotate said loop to vary itsinductive relation with said coil according to temperature changes,thereby to maintain the effective inductance of said coil substantiallyconstant.

2. In combination, a hollow coil' support, a helical coil mountedthereon, a U-shaped bracket embracing an edge portion of said support atone end thereof, the outer arm of said brecket having a slot therein, a.iastening screw extending through said slot and threadedly engaging anopening in said support, whereby said bracket may be adjusted to variouspositions. a rod carried by the inner arm of said bracket and extendingtransversely within said support, a. conductive loop rotatably carriedby said rod, and a thermaLresponsive spiral element surrounding said rodand having its ends connected respectively to the rod and to said loop,said element serving to rotate said loop to vary its inductive relationwith said coil according to temperature changes, thereby to maintain theeiective inductance of said coil substantially constant.

ELMER O. 'I'HOMPSON.

